[clang][Interp] Not all RVO call expressions are initializing

We do not necessarily prepare storage for the return value when
we are returning a complex value.

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -2703,7 +2703,14 @@ bool ByteCodeExprGen<Emitter>::VisitCallExpr(const CallExpr *E) {
           return false;
       }
     } else {
-      assert(Initializing);
+      // We need the result. Prepare a pointer to return or
+      // dup the current one.
+      if (!Initializing) {
+        if (std::optional<unsigned> LocalIndex = allocateLocal(E)) {
+          if (!this->emitGetPtrLocal(*LocalIndex, E))
+            return false;
+        }
+      }
       if (!this->emitDupPtr(E))
         return false;
     }

clang/test/AST/Interp/complex.cpp

@@ -124,6 +124,12 @@ void func(void) {
   result = arr * ii;
 }
 
+constexpr _Complex float getComplexFloat() {
+  return {1,2};
+}
+static_assert(__real(getComplexFloat()) == 1, "");
+static_assert(__imag(getComplexFloat()) == 2, "");
+
 namespace CastToBool {
   constexpr _Complex int F = {0, 1};
   static_assert(F, "");